This invention concerns particulate acid-functionalized polymeric compositions designed to impart enhanced corrosion resistance to substrates coated therewith by a fluidized bed process. When the polymers are semi-crystalline, enhanced creep resistance is imparted to the coating layer(s) by controlling both the degree of acid functionality and the degree to which there is crosslinking of the acid functionality. Although it is known to employ polymeric compositions to substrates by a fluidized bed process, such compositions and process have so far had limited success. The limitations have been caused, to a significant extent, by property deficiencies in the polymer-containing particulates employed in the fluidized bed. The particulate compositions, layered and hardened films, and coated substrates described herein and the processes for making and using them overcome the deficiencies that characterize materials known heretofore for use in fluidized bed technologies.
U.S. Pat. No. 4,739,011 discloses the use of a thermoplastic composition for injection molding, whereas the present invention relates to a coating which imparts corrosion resistance.
U.S. Pat. No. 4,849,264 discloses a one coat system that does not provide adhesion to subsequent decorative layers such as found in an automotive coating system as disclosed in the present invention.
U.S. Pat. No. 5,244,957 discloses the use of calcium sulfonate and a terpolymer composition containing acid groups but is not directed to a powder/particle coating composition and does not disclose the need for a select range of acid content for corrosion performance.
U.S. Pat. No. 5,411,809 discloses the use of epoxy/acid/anhydride systems as primer compositions, but does not disclose the importance of controlling the acid content for corrosion performance.
U.S. Pat. No. 5,470,893 discloses the use of a powder coating with both film forming and non-film forming components for specific decorative or performance attributes. However, these powder particles are not the uniformly blended film-formers of this invention with pigments and/or other additives uniformly distributed. Also, corrosion resistance is not disclosed in this patent.
U.S. Pat. No. 5,596,043 discloses the use of a powder coating as a primer in a multilayer system for improved chip performance. Corrosion performance as related to acid composition is not mentioned in this patent. Spherical polymer particles can be made by the procedure taught in U.S. Pat. No. 3,933,954.